Ammonium activation of zeolites in the presence of gaseous ammonia

ABSTRACT

Alumina-composited zeolite catalysts are activated by contact with an aqueous ammonium solution under ammonia gas pressure such that a pH of at least about 8 is maintained in the solution. The treated zeolite may thereafter be calcined without prior ammonium-exchange to provide the zeolite in the hydrogen form.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of copending U.S. applicationSer. No. 081,955, filed Aug. 5, 1987 now abandoned, the entiredisclosure of which is expressly incorporated herein by reference.

BACKGROUND

This invention relates to the activation of alumina-bound porouscrystalline silicate catalysts, e.g., zeolite catalysts, by contact withan aqueous ammonium solution under ammonia gas pressure such that a pHof at least about 8 is maintained in the solution. Zeolites deactivatedby steam or hydrocarbon conversion processes are particularly suited toactivation by the method of the present invention.

Methods for enhancing the catalytic activity of zeolitic materials arewell known, including treatments involving ammonium ion or ammonia. U.S.Pat. No. 4,326,994 relates to a process for enhancing acidic activity ofa highly siliceous zeolite by contact with steam and ammonia. Ammoniacalaluminum fluoride is taught as a reagent for zeolite activation in U.S.Pat. No. 4,427,788 while U.S. Pat. No. 3,684,738 discloses the treatmentof deactivated oxygen regenerated zeolites with a source of hydrogenions or hydrogen ion precursors such as an ammonium chloride solution.U.S. Pat. No. 4,427,788 teaches the use of aluminum fluoride in solutionwith at least one member selected from the group consisting of ammoniumhydroxide and ammonia. U.S. Pat. No. 4,500,419 teaches zeoliteactivation by treatment with hydrogen fluoride, followed by ammonolysis.All of the above references are incorporated herein by reference.

SUMMARY

It has now been found that the catalytic activity of an alumina-boundzeolite having a determinable initial activity can be increased bycontacting the zeolite with an aqueous ammonium solution under ammoniagas pressure such that a pH of at least about 8 is maintained in thesolution. The resulting zeolite can be calcined thereafter in order toconvert the zeolite to the hydrogen form without ammonium-exchangetreatment.

The present invention can also be described as a method for modifying acomposition to increase its acid catalytic activity. The compositioncomprises a solid source of aluminum such as an aluminum oxide binderand a zeolite having a constraint index of about 1 to 12. The method ofthe invention comprises contacting said composition with an aqueousammonium solution under ammonia gas pressure such that a pH of at leastabout 8, preferably at least about 10 is maintained in the solution. Acombination of conditions is maintained during this treatment so as toeffect an increase in catalytic activity. Such conditions can include atemperature of about 40° to 200° C., preferably about 100° to 150° C.for about 2 to 72 hours, preferably about 24 to 48 hours. The resultingcomposition may then be calcined in an inert or oxygen-containingatmosphere in order to place it in a catalytically active form withoutthe need for exposing the resulting composition to ammonium exchangeconditions. Calcination can take place at about 200° to 600° C.,preferably about 500° to 550° C., for about 1 minute to 48 hours,preferably about 0.5 to 6 hours. In one embodiment of the presentinvention, ammonium is provided to the aqueous ammonium solution by anammonium source selected from the group consisting of (NH₄)₂ CO₃, NH₄ OHand (NH₄)₂ HPO₄.

The catalyst which is activated by methods of the present invention maybe used, e.g., in a process for converting alcohols and/or ethers tohydrocarbons including aromatics. An example of a catalyst which can bereactivated by methods of the present invention is one which has becomedeactivated by a process for converting alcohols and/or ethers tohydrocarbons.

The aqueous ammonium solution employed for activating catalysts inaccordance with the method of the present invention may have an ammoniumconcentration of from about 0.001 to 10N, e.g., from about 0.01 to 10N,e.g., from about 0.1 to 5N (equivalents of ammonium ion/liter). Ammoniagas pressure employed may range, e.g., from about 20 to 1000 psig, e.g.,from about 80 to 500 psig. Contacting occurs under sufficient conditionsincluding, e.g., a temperature of about 40° to 200° C., e.g., about 100°to 150° C., for, e.g., about 2 to 72 hours, e.g., about 24 to 48 hours.

The contacting may also occur in the presence of a weak acid having apKa of at least about 2° at 25° C. Examples of such weak acids includeH₂ CO₃, H₃ BO₃, H₃ PO₄, acetic and citric acid. Alternatively, saidcontacting can occur in the presence of an alkylammonium hydroxide, suchas tetrapropylammonium hydroxide.

EMBODIMENTS

The catalyst composition treated by the method of the present inventionmay be one which has been previously utilized in an organic feedstock tohydrocarbon conversion under conditions sufficient to deactivate saidcomposition by removal of aluminum from said zeolite framework. Inanother aspect of the invention, the catalyst composition treated by thepresent method is one which has been previously contacted with steamunder conditions sufficient to deactivate the composition by removal ofaluminum from the zeolite framework. Such deactivation can occur underconditions of about 500° to 1700° F., for less than 1 hour to 1 week, at50 ppm H₂ O to 1 atm H₂ O, and an overall pressure of less than 1 atmpressure to 3000 atm.

Zeolitic materials, both natural and synthetic, have been demonstratedin the past to have catalytic properties for various types ofhydrocarbon conversion. Certain zeolitic materials are ordered, porous,crystalline aluminosilicates having a definite crystalline structure asdetermined by X-ray diffraction, within which there are a large numberof smaller cavities which may be interconnected by a number of stillsmaller channels or pores. These cavities and pores are uniform in sizewithin a specific zeolitic material. Since the dimensions of these poresare such as to accept for adsorption molecules of certain dimensionswhile rejecting those of larger dimensions, these materials have come tobe known as "molecular sieves" and are utilized in a variety of ways totake advantage of these properties.

Such molecular sieves, both natural and synthetic, include a widevariety of positive ion-containing crystalline aluminosilicates. Thesealuminosilicates can be described as a rigid three-dimensional frameworkof SiO₄ and AlO₄ in which the tetrahedra are cross-linked by the sharingof oxygen atoms whereby the ratio of the total aluminum and siliconatoms to oxygen atoms is 1:2. The electrovalence of the tetrahedracontaining aluminum is balanced by the inclusion in the crystal of acation, for example an alkali metal or an alkaline earth metal cation.This can be expressed wherein the ratio of aluminum to the number ofvarious cations, such as Ca/2, Sr/2, Na, K or Li, is equal to unity. Onetype of cation may be exchanged either entirely or partially withanother type of cation utilizing ion exchange techniques in aconventional manner. By means of such cation exchange, it has beenpossible to vary the properties of a given aluminosilicate by suitableselection of the cation. The spaces between the tetrahedra are occupiedby molecules of water prior to dehydration.

Prior art techniques have resulted in the formation of a great varietyof synthetic zeolites. The zeolites have come to be designated by letteror other convenient symbols, as illustrated by zeolite A (U.S. Pat. No.2,882,243), zeolite X (U.S. Pat. No. 2,882,244), zeolite Y (U.S. Pat.No. 3,130,007), zeolite beta (U.S. Pat. No. 3,308,069), zeolite ZK-5(U.S. Pat. No. 3,247,195), zeolite ZK-4 (U.S. Pat. No. 3,314,752),zeolite ZSM-5 (U.S. Pat. No. 3,702,886) ZSM-5/ZSM-11 intermediate (U.S.Pat. No. 4,229,424) zeolite ZSM-23 (U.S. Pat. No. 4,076,842), zeoliteZSM-11 (U.S. Pat. No. 3,709,979), zeolite ZSM-12 (U.S. Pat. No.3,832,449), zeolite ZSM-20 (U.S. Pat. No. 3,972,983) ZSM-35 (U.S. Pat.No. 4,016,245), ZSM-38 (U.S. Pat. No. 4,046,859), and zeolite ZSM-48(U.S. Pat. No. 4,375,573), merely to name a few. All of the abovepatents are incorporated herein by reference.

The silicon/aluminum atomic ratio of a given zeolite is often variable.For example, zeolite X can be synthesized with silicon/aluminum atomicratios of from 1 to 1.5; zeolite Y, from 1.5 to about 3. In somezeolites, the upper limit of the silicon/aluminum atomic ratio isunbounded. ZSM-5 is one such example wherein the silicon/aluminum atomicratio is at least 12. U.S. Pat. No. 3,941,871 (Re. 29,948) discloses aporous crystalline silicate made from a reaction mixture containing nodeliberately added aluminum in the recipe and exhibiting the X-raydiffraction pattern characteristic of ZSM-5 type zeolites. U.S. Pat.Nos. 4,061,724, 4,073,865 and 4,104,294 describe crystalline silicas ofvarying aluminum and metal content.

When zeolitic catalysts are utilized in organic conversion processestheir catalytic activity is often diminished when they are subjected todeactivating conditions such as steaming or oxygen regeneration whichare believed to result in displacement of aluminum from the zeoliteframework. Highly siliceous aluminosilicate zeolites are particularlysusceptible to such deactivation because they initially contain onlyrelatively small amounts of aluminum in the framework. Accordingly, thepresent invention while suitable for aluminosilicates in general, isparticularly useful in the activation of highly siliceous zeolites,i.e., zeolites having a silica to alumina molar ratio of at least about12, say, at least about 100, e.g., at least about 500 or even at leastabout 800.

Large pore size zeolites having a constraint index (C.I.) of less than1, e.g., zeolites X, Y, mordenite, Ultrastable Zeolite Y (USY) andZSM-20, can be activated by the method of the present invention.Intermediate pore size zeolites having a constraint index of about 1 to12, e.g., ZSM-5, ZSM-5/ZSM-11 intermediate, ZSM-12, ZSM-23, ZSM-35,ZSM-38 and ZSM-48, are also suitable for treatment by the method of thepresent invention. An important characteristic of the crystal structureof these intermediate pore size crystalline aluminosilicates is thatthey provide constrained access to, and egress from, theintracrystalline free space by virtue of having a pore dimension greaterthan about 5 Angstroms and pore windows of about a size such as would beprovided by 10 membered rings of oxygen atoms. It is to be understood,of course, that these rings are those formed by the regular dispositionof the tetrahedra making up the anionic framework of the crystallinealuminosilicate, the oxygen atoms themselves being bonded to the siliconor aluminum atoms at the centers of the tetrahedra. Briefly, thepreferred zeolites useful in this invention possess, in combination, asilica to alumina mole ratio of at least about 12; and a structureproviding constrained access to the crystalline free space.

The members of this class of intermediate pore size zeolites have aneffective pore size of generally from about 5 to about 8 angstroms suchas to freely sorb normal hexane. In addition, the structure must provideconstrained access to larger molecules. It is sometimes possible tojudge from a known crystal structure whether such constrained accessexists. For example, if the only pore windows in a crystal are formed by8-membered rings of silicon and aluminum atoms, then access by moleculesof larger cross-section than normal hexane is excluded and the zeoliteis not of the desired type. Windows of 10-membered rings are preferred,although, in some instances, excessive puckering of the rings or poreblockage may render these zeolites ineffective.

Although 12-membered rings in theory would not offer sufficientconstraint to produce advantageous conversions, it is noted that thepuckered 12-ring structure of TMA offretite does show some constrainedaccess. Other 12-ring structures may exist which may be operative forother reasons, and therefore, it is not the present intention toentirely judge the usefulness of the particular porous crystallinesilicate solely from theoretical structural considerations.

A convenient measure of the extent to which a zeolite provides controlto molecules of varying sizes to its internal structure is theConstraint Index of the porous crystalline silicate. Porous crystallinealuminosilicates which provide a highly restricted access to and egressfrom its internal structure have a high value for the Constraint Index,and zeolites of this kind have pores of small size, e.g., less than 5angstroms. On the other hand, porous crystalline aluminosilicates whichprovide relatively free access to the internal porous crystallinesilicate structure have a low value for the Constraint Index, andusually pores of large size, e.g., greater than 8 angstroms. This methodby which Constraint Index is determined is described fully in U.S. Pat.No. 4,016,218, incorporated herein by reference for details of themethod.

Constraint Index (CI) values for some typical materials are:

    ______________________________________                                                       CI (at test temperature)                                       ______________________________________                                        ZSM-4            0.5      (316° C.)                                    ZSM-5            6-8.3    (371° C.-316° C.)                     ZSM-11           5-8.7    (371° C.-316° C.)                     ZSM-12           2.3      (316° C.)                                    ZSM-20           0.5      (371° C.)                                    ZSM-22           7.3      (427° C.)                                    ZSM-23           9.1      (427° C.)                                    ZSM-34           50       (371° C.)                                    ZSM-35           4.5      (454° C.)                                    ZSM-38           2        (510° C.)                                    ZSM-48           3.5      (538° C.)                                    ZSM-50           2.1      (427° C.)                                    TMA Offretite    3.7      (316° C.)                                    TEA Mordenite    0.4      (316° C.)                                    Clinoptilolite   3.4      (510° C.)                                    Mordenite        0.5      (316° C.)                                    REY              0.4      (316° C.)                                    Amorphous Silica-alumina                                                                       0.6      (538° C.)                                    Dealuminized Y   0.5      (510° C.)                                    Erionite         38       (316° C.)                                    Zeolite Beta     0.6-2.0  (316° C.-399° C.)                     ______________________________________                                    

It should be noted that Constraint Index seems to vary somewhat withseverity of operations (conversion) and the presence or absence ofbinders. Likewise, other variables, such as crystal size of the zeolite,the presence of occluded contaminants, etc., may affect the ConstraintIndex. Therefore, it will be appreciated that it may be possible to soelect test conditions, e.g., temperature, as to establish more than onevalue for the Constraint Index of a particular porous crystallinealuminosilicate. This explains the range of Constraint Indices for somezeolites, such as ZSM-5, ZSM-11 and Beta.

It is to be realized that the above CI values typically characterize thespecified porous crystalline aluminosilicates, but that such are thecumulative result of several variables useful in the determination andcalculation thereof. Thus, for a given zeolite exhibiting a CI valuewithin the range of 1 to 12, depending on the temperature employedduring the test method within the range of 290° C. to about 538° C.,with accompanying conversion between 10% and 60%, the CI may vary withinthe indicated range of 1 to 12. Likewise, other variables such as thecrystal size of the porous crystalline aluminosilicate, the presence ofpossibly occluded contaminants and binders intimately combined with thezeolite may affect the CI. It will accordingly be understood to thoseskilled in the art that the CI, as utilized herein, while affording ahighly useful means for characterizing certain porous crystallinealuminosilicates of interest is approximate, taking into considerationthe manner of its determination, with the possibility, in someinstances, of compounding variable extremes.

The zeolitic catalyst composition of the invention comprises analuminum-containing matrix material normally resistant to thetemperature and other conditions employed in a chemical conversionprocess. Such matrix material is useful as a binder and imparts greaterresistance to the catalyst for the severe temperature, pressure andreactant feed stream velocity conditions encountered in many processes,such as, for example, cracking. Useful matrix materials include bothsynthetic and naturally occurring substances, as well asaluminum-containing inorganic materials such as clay and/or metaloxides, e.g., alumina. The latter may be either naturally occurring orin the form of gelatinous precipitates or gels including mixtures ofsilica and metal oxides. Naturally occurring clays which can becomposited with the zeolite include those of the montmorillonite andkaolin families, which families include the sub-bentonites and thekaolins commonly known as Dixie, McNamee, Georgia and Florida clays orothers in which the main mineral constituent is halloysite, kaolinite,dickite, nacrite or anauxite. Such clays can be used in the raw state asoriginally mined or initially subjected to calcination, acid treatmentor chemical modification.

In addition to the foregoing materials, the zeolites employed herein maybe composited with a porous matrix material, such as silica-alumina,ternary compositions, such as silica-alumina-thoria,silica-alumina-zirconia, and silica-alumina-magnesia. The matrix may bein the form of a cogel. The relative proportions of zeolite componentand inorganic matrix, on an anhydrous basis, may vary widely with thezeolite content ranging from about 1 to about 99 percent by weight andmore usually in the range of from about 5 to about 80 percent by weightof the dry composite.

In general, organic compounds such as, for example, those selected fromthe group consisting of hydrocarbons, alcohols and ethers, are convertedto conversion products such as, for example, aromatics and lowermolecular weight hydrocarbons, over the catalyst composition activated adescribed above by contact under organic compound conversion conditions.Such conditions may include a temperature of from about 100° C. to about800° C., a pressure of from about 0.1 atmosphere (bar) to about 200atmospheres, a weight hourly space velocity of from about 0.08 hr⁻¹ toabout 2000 hr⁻¹ and a hydrogen/feedstock organic, e.g., hydrocarbon,compound mole ratio of from 0 (no added hydrogen) to about 100.

Such conversion processes include, as non-limiting examples, crackinghydrocarbons with reaction conditions including a temperature of fromabout 300° C., to about 700° C., a pressure of from about 0.1 atmosphere(bar) to about 30 atmospheres and a weight hourly space velocity of fromabout 0.1 to about 20; dehydrogenating hydrocarbon compounds withreaction conditions including a temperature of from about 300° C. toabout 700° C., a pressure of from about 0.1 atmosphere to about 10atmospheres and a weight hourly space velocity of from about 0.1 toabout 20; converting paraffins to aromatics with reaction conditionsincluding a temperature of from about 100° C. to about 700° C., apressure of from about 0.1 atmosphere to about 60 atmospheres, a weighthourly space velocity of from about 0.5 to about 400 and ahydrogen/hydrocarbon mole ratio of from about 0 to about 20; convertingolefins to aromatics, e.g., benzene, toluene and xylenes, with reactionconditions including a temperature of from about 100° C. to about 700°C., a pressure of from about 0.1 atmosphere to about 60 atmospheres, aweight hourly space velocity of from about 0.5 to about 400 and ahydrogen/hydrocarbon mole ratio of from about 0 to about 20; convertingalcohols, e.g., methanol, or ethers, e.g., dimethylether, or mixturesthereof to hydrocarbons including aromatics with reaction conditionsincluding a temperature of from about 275° C. to about 600° C., apressure of from about 0.5 atmosphere to about 50 atmospheres and aliquid hourly space velocity of from about 0.5 to about 100; isomerizingxylene feedstock components with reaction conditions including atemperature of from about 230° C. to about 510° C., a pressure of fromabout 3 atmospheres to about 35 atmospheres, a weight hourly spacevelocity of from about 0.1 to about 200 and a hydrogen/hydrocarbon moleratio of from about 0 to about 100; disproportionating toluene withreaction conditions including a temperature of from about 200° C. toabout 760° C., a pressure of from about atmospheric to about 60atmospheres and a weight hourly space velocity of from about 0.08 toabout 20; alkylating aromatic hydrocarbons, e.g., benzene andalkylbenzenes, in the presence of an alkylating agent, e.g., olefins,formaldehyde, alkylhalides and alcohols, with reaction conditionsincluding a temperature of from about 340° C. to about 500° C., apressure of from about atmospheric to about 200 atmospheres, a weighthourly space velocity of from about 2 to about 2000 and an aromatichydrocarbon/alkylating agent mole ratio of from about 1/1 to about 20/1;and transalkylating aromatic hydrocarbons in the presence ofpolyalkylaromatic hydrocarbons with reaction conditions including atemperature of from about 290° C. to about 500° C., a pressure of fromabout atmospheric to about 200 atmospheres, a weight hourly spacevelocity of from about 10 to about 10000 and an aromatichydrocarbon/polyalkylaromatic hydrocarbon mole ratio of from about 1/1to about 16/1.

In order to more fully illustrate the nature of the invention and themanner of practicing same, the following examples are presented. In theexamples, whenever Alpha Value is examined, it is noted that the AlphaValue is an approximate indication of the catalytic cracking activity ofthe catalyst compared to a standard catalyst and it gives the relativerate constant (rate of normal hexane conversion per volume of catalystper unit time). It is based on the activity of the highly activesilica-alumina cracking catalyst taken as an Alpha of 1 (RateConstant=0.016 sec ⁻¹). The Alpha Test is described in U.S. Pat. No.3,354,078 and in The Journal of Catalysis, Vol. IV, pp. 527-529 (August1965), each incorporated herein by reference as to that description.Alpha Tests are also described in J. Catalysis, 6, 278 (1966) and J.Catalysis, 61, 395 (1980), which are also incorporated herein byreference.

Example 1

An extrudate consisting of 65 weight percent H-ZSM-5 having a SiO₂ /Al₂O₃ ratio of about 880, and 35 weight percent Al₂ O₃, and having an alphavalue of 4 was treated with various NH₄ + solutions in an autoclave with80 psig NH₃. The results are summarized in Table 1. With a 0.5N (NH₄)₂CO₃ solution at 50° C. for 3 days, no significant change in crackingactivity was observed. When the temperature was increased to 100° C.,the alpha value increased to 15. With a higher concentration solution of1N, 20 hours treatment increased the alpha to 84. With 1N NH₄ OHsolution at 100° C. for 20 hours, the alpha increased to 95. With1N(NH₄)₂ HPO₄ solution at 100° C. for 20 hours, alpha increased to 39.

Example 2

An order to study the effects of increasing the concentration of NH₃ insolution, higher ammonia pressure was applied. Table 2 sets out theresults of NH₃ treatment at 80 and 1000 psig of the extrudate of Example1 as well as an extrudate having an SiO₂ /Al₂ O₃ ratio of 520. Theresults show the high pressure process gives lower activation asmeasured by the alpha test. The crystallinity calculated by n-C₆sorption agrees with the crystallinity obtained by X-ray diffraction(XRD). This may be an indication that very little dissolution of thecrystals occurs when treated by the present process.

Example 3

Table 3 sets out the results of two unbound high SiO₂ /Al₂ O₃ ZSM-5zeolites (880 and 520) treated with NH₃ for 20 and 72 hours. The alphaof the zeolite remained unchanged indicating that no activation occurredin the absence of alumina binder. Accordingly, it is believed that theNH₃ treatment causes little structural damage to zeolites.

                  TABLE 1                                                         ______________________________________                                        Treatment of ZSM-5 Extrudate (SiO.sub.2 /Al.sub.2 O.sub.3 = 880)              100° C. for 20 hours                                                   NH.sub.3 Pressure = 80 psig                                                   Treatment   Conc.       Time (hr) Alpha                                       ______________________________________                                        --          --          --        4                                           (NH.sub.4).sub.2 CO.sub.3                                                                 0.5 N       3 days*   6                                           (NH.sub.4).sub.2 CO.sub.3                                                                 0.5 N       20        15                                          (NH.sub.4).sub.2 CO.sub.3                                                                 1 N         20        84                                          (NH.sub.4).sub.2 HPO.sub.4                                                                1 N         20        39                                          NH.sub.4 OH 1 N         20        95                                          ______________________________________                                         *at 50° C.                                                        

                  TABLE 2                                                         ______________________________________                                        Activation of High SiO.sub.2 /Al.sub.2 O.sub.3 ZSM-5 Extrudate                100° C.                                                                NH.sub.3 Pressure = 80 and 1000 psig                                          ______________________________________                                        SiO.sub.2 /Al.sub.2 O.sub.3 = 880                                             Time (hr)   --          20      20                                            NH.sub.3 P (psig)                                                                         --          80      1000                                          Alpha       4           95      44                                            n-C.sub.6 sorp (%)                                                                        7.90        5.43    5.26                                          Δn-C.sub.6 sorp (%)                                                                 100         69      67                                            XRD (%)     100         69      69                                            SiO.sub.2 /Al.sub.2 O.sub.3 = 520                                             Time (hr)   --          20      20                                            NH.sub.3 P (psig)                                                                         --          80      1000                                          Alpha       16          193     109                                           n-C.sub.6 sorp (%)                                                                        7.24        5.23    4.49                                          Δn-C.sub.6 sorp (%)                                                                 100         72      62                                            XRD (%)     100         71      61                                            ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        Activation of High SiO.sub.2 /Al.sub.2 O.sub.3 ZSM-5                          100° C.                                                                Form        extrudate   zeolite zeolite                                       ______________________________________                                        NH.sub.3 Pressure = 80 psig                                                   Time (hr)   20          20      72                                            Alpha (initial)                                                                           16          16      16                                            Alpha (final)                                                                             193         15      16                                            NH.sub.3 Pressure = 1000 psig                                                 Time (hr)   20          20      72                                            Alpha (initial)                                                                           16          16      16                                            Alpha (final)                                                                             109         18      14                                            ______________________________________                                    

Example 4

A fresh catalyst containing 65 wt. % ZSM-5 and 35 wt. % alumina binderwas deactivated while using the catalyst in a process for convertingmethanol to hydrocarbons, particularly gasoline boiling rangehydrocarbons including aromatics. The silica to alumina molar ratio ofthe ZSM-5 in the fresh catalyst was 70:1. Coke was removed from thedeactivated catalyst by calcining the catalyst in air for 12 hours at538° C. This calcination removed 6 wt. % coke and gave a spent catalystwith an alpha value of 8. This spent catalyst was reactivated bytreatment in a sealed vessel for 20 hr. at 100° C. with 10 mol % aqueousammonium hydroxide, washed with deionized water, dried at 110° C. andcalcined at 538° C. The alpha value of the reactivated sample was 70.

Example 5

The reactivated catalyst of Example 4 was used for methanol to gasolineconversion at 4 WHSV 83% methanol, 440° C. hot spot temperature, 300psig, 9:1 molar He:methanol feed. Table 4 shows product distributionsfrom methanol conversion over the first cycle, which lasted 4.5 days tomethanol breakthrough. By way of comparison, the first cycle over thefresh catalyst lasted for 5.4 days to methanol breakthrough. The totalfirst cycle C5+ hydrocarbon yield for the reactivated catalyst was 75%of that for fresh catalyst. The calcined spent catalyst mentioned inExample 4, prior to reactivation lasted less than one hour untilmethanol breakthrough.

                  TABLE 4                                                         ______________________________________                                        Aging Test                                                                    ______________________________________                                        Time on Stream, hrs.                                                                           5       52      76   108                                     Selectivity to hydrocarbons,                                                                   32.9    34.9    33.6 34.2                                    wt. %                                                                         Aromatics, wt. % 13.0    10.1    10.7 10.2                                    C.sub.5 + hydrocarbons/                                                                        71.6    67.0    73.0 71.7                                    total hydrocarbons, wt. %                                                     Methanol, wt. %  0.0     0.0     0.0  0.1                                     Water, wt. %     67.1    65.1    66.4 65.7                                    Dimethylether, wt %                                                                            0.0     0.0     0.0  0.0                                     ______________________________________                                    

It is claimed:
 1. A method for modifying a composition to increase itsacid catalytic activity, said composition comprising a solid source ofaluminum and a zeolite characterized by a silica to alumina mole ratioof at least about 100 and a constraint index of about 1 to 12, whichmethod comprises contacting said composition with an aqueous ammoniumsolution under ammonia gas pressure such that a pH of at least about 8is maintained in said solution and under a combination of conditionsincluding a temperature of about 40° to 200° C. for about 2 to 72 hours,said combination of conditions being effective to induce said increasein catalytic activity.
 2. The method of claim 1 wherein said resultingcomposition is calcined.
 3. The method of claim 2 wherein said ammoniumis provided by an ammonium source selected from the group consisting of(NH₄)₂ CO₃, NH₄ OH and (NH₄)₂ HPO₄.
 4. The method of claim 3 whereinsaid silica to alumina mole ratio is at least about
 500. 5. The methodof claim 4 wherein said zeolite has a structure selected from the groupconsisting of ZSM-5, ZSM-5/ZSM-11, ZSM-11, ZSM-12, ZSM-23, ZSM-35,ZSM-38, ZSM-48 and zeolite beta.
 6. The method of claim 5 wherein saidaqueous ammonium solution has an ammonium concentration of about 1 to10N.
 7. The method of claim 6 wherein said ammonia gas pressure rangesfrom about 40 to 1000 psig.
 8. The method of claim 7 wherein saidzeolite is combined with an inorganic oxide matrix.
 9. The method ofclaim 8 wherein said contacting occurs at a temperature ranging fromabout 40° to 200° C.
 10. The method of claim 9 wherein said contactingoccurs in the presence of a weak acid having a pKa of at least about 2at 25° C.
 11. The method of claim 9 wherein said contacting occurs inthe presence of an alkylammonium hydroxide.
 12. The method of claim 9wherein said ammonium source is NH₄ OH.
 13. The method of claim 9wherein said zeolite has the structure of ZSM-5.
 14. The method of claim13 wherein said aqueous ammonium ion solution has an ammoniumconcentration of about 1N to 10N.
 15. The method of claim 14 whereinsaid ammonia gas pressure ranges from about 80 to 1000 psig.
 16. Themethod of claim 15 wherein said inorganic matrix is alumina.
 17. Themethod of claim 16 wherein said contacting occurs at a temperatureranging from about 100° to 150° C.
 18. The method of claim 10 whereinsaid contacting occurs in the presence of a weak acid selected from thegroup consisting of H₂ CO₃, H₃ BO₃ and citric acid.
 19. The method ofclaim 11 wherein said alkylammonium hydroxide is tetrapropylammoniumhydroxide.
 20. The method of claim 1 wherein said zeolite is calcinedafter said contacting.